In general, with an increasing demand for a broadband, as user access lines, implementation of large-capacity access lines has been advanced instead of a communication technology based on a telephone line such as a digital subscriber line (DSL). At present, in the optical access lines, a passive optical network (PON) system that can share optical fibers with plural subscribers has been frequently used from line construction costs and maintenance management costs. The PON system that multiplexes traffics flowing between a plurality of users and a station so that a connection status and a bandwidth usage situation can be intensively managed at the station side is one of major technologies in the future subscriber line service.
In the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) that is one of international standardization organizations, a gigabit capable PON (G-PON) system is specified (Non Patent Literatures 1 to 3). In 2006, a large number of vendors have started to supply G-PON products to the market, and at the same time, carriers in the respective countries have started optical access services employing the G-PON. Also, parts of the carriers are providing the optical access services employing a gigabit Ethernet (registered trademark) PON (GE-PON) (Non Patent Literature 4) specified by the Institute of Electrical and Electronics Engineers, Inc. (IEEE) which is another international standardization organization.
In the transmission network, a study has been made to shift from the existing synchronous optical network (SONET)/synchronous digital hierarchy (SDH) technology and the asynchronous transfer mode (ATM) technology to a packet communication technology such as the Ethernet and multi-protocol label switching (MPLS). In the packet communication network, a packet format is configured by a header and a payload, and a relay unit conducts processing for each packet on the basis of a destination ID and a source ID included in a header part as well as associated control information. In this case, a communication configuration is not of a system that transmits and receives a signal with the aid of a statically set path such as the existing synchronous network or ATM network, but of a communication system different in the communication path for each packet. When attention is paid to a part of the paths, a series of packets having the same header information do not occupy the path, but plural packets having the respective different header information exist on the path at the same time.
At present, the communication network is becoming essential as the society's infrastructure. With wide spread of the communication network, a demand has been made to reduce the price of the communication servicer. It would be substantially obvious that this tendency leads to such an idea that the infrastructure is configured by the combination of the optical access network and the packet communication network. On the other hand, high stability is required to provide the infrastructure. The development of the maintenance and management function for improving the stability causes an increase in the costs.
As one method for satisfying conflicting requirements such as realization for the low price and the securement for the high stability, a method has been studied in which in order to artificially maintain and manage the path in the packet communication, a virtual local area network (VLAN) in the Ethernet and a label switched path (LSP) in the MPLS are set to manage the connection. Such an idea that the path is artificially set on the packet communication network, and the path is maintained and managed is useful in coexistence with the existing network and shift from the existing network. As a typical example thereof, there is an Ethernet operations, administration and maintenance (OAM) technology (Non Patent Literature 5). Further, a protection switching technology based on the Ethernet OAM (Non Patent Literature 6) is standardized.    Non Patent Literature1: ITU-T Recommendation G.984.1, “Gigabit-capable Passive Optical Networks(G-PON): General Characteristics”    Non Patent Literature2: ITU-T Recommendation G.984.2, “Gigabit-capable Passive Optical Networks (G-PON): Physical Media Dependent (PMD) Layer Specification”    Non Patent Literature3: ITU-T Recommendation G.984.3, “Gigabit-capable Passive Optical Networks (G-PON): Transmission convergence Layer Specification”    Non Patent Literature4: IEEE 802.3-2005, “IEEE Standard for Information Technology-Telecommunications and Information exchange between Systems-Local and Metropolitan Area Networks—Specific Requirements Part 3: Carrier Sense Multiple Access With Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications”    Non patent Literature5: ITU-T Recommendation Y.1731, “OAM Functions and Mechanisms for Ethernet based Networks”    Non Patent literature6: ITU-T Recommendation G.8031/Y.1342, “Ethernet Protection Switching”    Non Patent Literature7: ITU-T Recommendation G.8021, “Characteristics of Ethernet transport network equipment functional blocks”